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Re: [Qemu-devel] [PATCH qemu v14 17/18] vfio/spapr: Use VFIO_SPAPR_TCE_v

From: Alexey Kardashevskiy
Subject: Re: [Qemu-devel] [PATCH qemu v14 17/18] vfio/spapr: Use VFIO_SPAPR_TCE_v2_IOMMU
Date: Thu, 24 Mar 2016 11:03:31 +1100
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.0

On 03/23/2016 05:03 PM, David Gibson wrote:
On Wed, Mar 23, 2016 at 02:06:36PM +1100, Alexey Kardashevskiy wrote:
On 03/23/2016 01:53 PM, David Gibson wrote:
On Wed, Mar 23, 2016 at 01:12:59PM +1100, Alexey Kardashevskiy wrote:
On 03/23/2016 12:08 PM, David Gibson wrote:
On Tue, Mar 22, 2016 at 04:54:07PM +1100, Alexey Kardashevskiy wrote:
On 03/22/2016 04:14 PM, David Gibson wrote:
On Mon, Mar 21, 2016 at 06:47:05PM +1100, Alexey Kardashevskiy wrote:
New VFIO_SPAPR_TCE_v2_IOMMU type supports dynamic DMA window management.
This adds ability to VFIO common code to dynamically allocate/remove
DMA windows in the host kernel when new VFIO container is added/removed.

This adds VFIO_IOMMU_SPAPR_TCE_CREATE ioctl to vfio_listener_region_add
and adds just created IOMMU into the host IOMMU list; the opposite
action is taken in vfio_listener_region_del.

When creating a new window, this uses euristic to decide on the TCE table
levels number.

This should cause no guest visible change in behavior.

Signed-off-by: Alexey Kardashevskiy <address@hidden>
* new to the series

* export levels to PHB
  hw/vfio/common.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++++---
  trace-events     |   2 ++
  2 files changed, 105 insertions(+), 5 deletions(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 4e873b7..421d6eb 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -279,6 +279,14 @@ static int vfio_host_iommu_add(VFIOContainer *container,
      return 0;

+static void vfio_host_iommu_del(VFIOContainer *container, hwaddr min_iova)
+    VFIOHostIOMMU *hiommu = vfio_host_iommu_lookup(container, min_iova, 

The hard-coded 0x1000 looks dubious..

Well, that's the minimal page size...

Really?  Some BookE CPUs support 1KiB page size..

Hm. For IOMMU? Ok. s/0x1000/1/ should do then :)

Uh.. actually I don't think those CPUs generally had an IOMMU.  But if
it's been done for CPU MMU I wouldn't count on it not being done for

1 is a safer choice.

+    g_assert(hiommu);
+    QLIST_REMOVE(hiommu, hiommu_next);
  static bool vfio_listener_skipped_section(MemoryRegionSection *section)
      return (!memory_region_is_ram(section->mr) &&
@@ -392,6 +400,61 @@ static void vfio_listener_region_add(MemoryListener 
      end = int128_get64(llend);

+    if (container->iommu_type == VFIO_SPAPR_TCE_v2_IOMMU) {

I think this would be clearer split out into a helper function,
vfio_create_host_window() or something.

It is rather vfio_spapr_create_host_window() and we were avoiding
xxx_spapr_xxx so far. I'd cut-n-paste the SPAPR PCI AS listener to a
separate file but this usually triggers more discussion and never ends well.

+        unsigned entries, pages;
+        struct vfio_iommu_spapr_tce_create create = { .argsz = sizeof(create) 
+        g_assert(section->mr->iommu_ops);
+        g_assert(memory_region_is_iommu(section->mr));

I don't think you need these asserts.  AFAICT the same logic should
work if a RAM MR was added directly to PCI address space - this would
create the new host window, then the existing code for adding a RAM MR
would map that block of RAM statically into the new window.

In what configuration/machine can we do that on SPAPR?

spapr guests won't ever do that.  But you can run an x86 guest on a
powernv host and this situation could come up.

I am pretty sure VFIO won't work in this case anyway.

I'm not.  There's no fundamental reason VFIO shouldn't work with TCG.

This is not about TCG (pseries TCG guest works with VFIO on powernv host),
this is about things like VFIO_IOMMU_GET_INFO vs.
VFIO_IOMMU_SPAPR_TCE_GET_INFO ioctls but yes, fundamentally, it can work.

Should I add such support in this patchset?

Unless adding the generality is really complex, and so far I haven't
seen a reason for it to be.

Seriously? :(


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